Spray dryer air flow control

ABSTRACT

An apparatus and method for providing a uniform cross-sectional air flow for the drying chambers of tunnel-type tray and spray dryers and the freezing chambers of blast freezers by placing guide members having air directing orifices positioned over their surfaces adjacent to the air inlets and outlets of said chambers. Means are provided to introduce the material to be treated and a stream of heated air into the chambers.

llriited Mates Patent Merge um 1 Mar, M, W72

[54] SlPll'fiAlI DRYER MIR IFILU'W CUW'JTMUL 2,576,264 11/1951 2,851,0979/1958 [72] Inventor. Dwight H. lfiergquust, Springfield, Mo. 2,893,8717/1959 [73] Assignee: llllennilngsen Foods, line, White Plains, 13,06212/1963 NY, 3,415,665 12/1968 Hussmann ..159/48 [22] Filed: 1969 PrimaryExaminer-Norman Yudkoff [2 Appl 349 92 Assistant Examiner-J. SoferAltorney Norman N. Holland [52] US. Cl. ..159/4, 159/4 F;4 C, 34/227;233[57] ABSTRACT [51] lnLCl ..lllllld 11/16 581 Wield or Search ..159/48,48 L, 4 F, 4 c, 4 E, apparatus and method Pmvdmg 3 cross-Sec 159/434/146 233 1 16418 227 tional air flow for the drying chambers oftunnel-type tray and spray dryers and the freezing chambers of blastfreezers by r placing guide members having air directing orificespositioned [J6] Referemes (Med over their surfaces adjacent to the airinlets and outlets of said UNITED STATES PATENTS chambers. Means areprovided to introduce the material to be treated and a stream of heatedair into the chambers. 2,363,281 11/1944 Arnold ..34/10 502,237 7/1893Proctor ..34/196 X 2 Claims, 8 Drawing Figures KBLOWE/Q HEATER 5 F/L meSlPlltAlf DllttlEllll Allllt FLOW CONTROL BACKGROUND OF THE INVENTIONUniform cross-sectional air flow has been difficult to achieve intunnel-type tray dryers, spray dryers, and blast freezers. Air flow hasbeen found to be non-uniform in the ar ticle treating chambers of thesepieces of equipment, and this has created many problems as discussedbelow. The purpose of this invention is to provide a method andapparatus for obtaining uniform cross'sectional air flow through anarticle drying or freezing chamber. The term article treating chamber isused to cover the drying and freezing chambers mentioned above.

In tunnel-type tray dryers, non-uniform air flow results in over-dryingof some materials and under-drying of other materials depending on theirlocation in the tunnel. In order to dry the material that is in the lowair flow region, drying times have to be extended or temperatures haveto be increased to remove moisture from the slowest drying materials.Material in the high air flow regions then becomes over-dried and overheated. Uniform cross-sectional air flow minimizes heat exposure anddrying time by allowing all of the material to dry at the same rateregardless of its location in the cross section of the tunnel.

In the spray dryers, air flow is usually very complex and non-uniform.There are many different designs for spray drying equipment, but none ofthe prior designs provide suitably uniform cross-sectional air flowthrough the drying chamber. Non-unifomi air flow and eddy currentsresulting from an abrupt entrance of the drying air into and exit fromthe drying chambers give differences in drying conditions at differentlocations and also cause depositing of material on the walls of thechamber. Here again, drying conditions have to be adjusted to fully drythe particles in the zones of the poorest dry ing conditions at the riskof heat damage to particles in other zones. Thus, in the improved methodand means, drying temperatures can be at a minimum and heat sensitiveproducts can be dried with a minimum risk of damage to their desirablefunctional and chemical properties. Because the air flow is uniform,there is also little or no buildup of product on the chamber walls.

The advantage of uniform cross-sectional air flow can also bedemonstrated in other equipment, such as in blast freezers. Here uniformcross-sectional air flow through the freezing chamber results in auniform freezing of all materials placed in the air stream.

DESCRIPTION OF THE INVENTION Uniform cross-sectional air flow insuresthat the velocity of air moving through a chamber is substantially thesame at any point in the chamber cross section except for areasimmediately at the surfaces of the walls, floors and ceilings. Uniformcross-sectional air flow is achieved by using flow directing platesthrough which there is a substantial air pres sure drop. This orificeplate or member is placed at both the inlet cross section and outletcross section of the chamber through which the air flows in order toachieve maximum uniformity in the cross-sectional flow through theentire length of the chamber. The orifice plates preferably cover theentire cross section of the inlets and outlets of the chambers and theorifices are preferably spaced uniformly throughout the plate.

The cross-sectional shape of the chamber may be either square,rectangular, circular or oval. The crosssectional area and shape shouldbe the same throughout the entire length of the chamber.

A preferred embodiment of the present invention has been chosen forpurposes of illustration and is shown in the drawings wherein:

FIG. I is a partially cut away perspective view of the invention as usedin a tunnel-type tray dryer;

FIG. 2 is a fragmentary sectional view of FIG. ll showing a rack ofarticles being tray dried;

FIG. 3 is a front view of an orificed air plate that is positioned atthe inlet and outlet of the drying or freezing chamber;

FIG. 4, is a perspective view of another embodiment illustrating a spraydryer;

FIG. 5 is a vertical sectional view of the dryer of FIG. 4 taken alongline 5-5 on FIG. ll;

FIG. n is a sectional view of the dryer taken along line 6-6 on FIG. 5;

FIG. 7 is a side elevational view partially in section of anotherembodiment of a spray dryer having a vertical drying chamber; and

FIG. g is a horizontal sectional view taken along line fl-8 on FIG. 7.

The invention may be used in conjunction with the tunneltype tray dryerIt) such as illustrated in FIGS. 1 and 2 of the drawings. The dryer It)consists of a drying chamber 1 having an air inlet Ma at one end an airoutlet Mb at the other. The inlet Ma and the outlet Mlb are covered byplates lla and Alb, respectively, having a plurality of orifices 5therein proportioned and spaced as described above. FIG. 3 is a view ofa preferred form of the plates in greater detail. It can be seen thatthe plate comprises a relatively flat member having a large number ofapertures or orifices 5 uniformly spaced throughout. Plate do completelycovers the inlet Ma and plate ilb covers the outlet Mb of the dryingchamber 1. Racks 6 containing material on trays 7 are introduced intothe drying chamber ll through a suitable inlet b closed by a door orcovering do after the rack b is introduced. The trays 7 are convenientlyarranged in horizontal layers and 3-inch separation between the trays 7has been found to be satisfactory. The heated air is moved through thesystem by a blower 9 and flared entry MI. The air is exhausted throughoutlet ill. It has been found that the velocity of the air flow isuniform through the chamber I cross section.

In commercial size dryers where the drying chamber is several feet indiameter and several times as long as it is wide, a satisfactory orificepattern comprises holes of from about one quarter inch to about one inchin diameter and spaced on centers about three hole radii apart.

A desired uniform air flow exists between such orifice plates when theoverall air pressure drop through the chamber including the two orificeplates is greater than about 1 inch water so that the pressure dropacross each orifice plate is greater than about 0.5 inch water.

Pressure drops of this amount may be obtained with orifice or air flowcontrol plates having smaller orifices than those described above, suchas screen-like plates where the ratio of the apertured area to the solidarea is arranged to give the desired uniform air pressure drops in theflow of drying air.

This invention has also been found to be particularly useful in anotherembodiment where the drying operation is performed by spray drying.FIGS. 41, 5 and 6 illustrate a preferred embodiment of this system. Thedryer 20 includes an elongated drying chamber 21 having its flared inlet22 connected to a source 23 of hot and filtered air including a blower24L The chamber 2i includes a tapered outlet 25 for the dried materialwhich is alternatively coupled to either a cyclone collector 26 or to abag collector 27. The cyclone collector 2b, of the type commerciallyavailable for collecting powdered material, may be used for mostproducts. In certain situations where almost no product loss can betolerated or where extremely minute particles are being processed, amore efficient bag-type air filter collector may be used. Tracks 2% areillustrated over which the alternative collector means may be moved intoposition and coupled to the dryer tunnel outlet 25.

An extremely uniform laminar flow of the hot drying air through thedrying chamber is obtained in the preferred embodiment through the useof orifice plates 29 and 30 of the chamber inlet and outlet 22 and 25,respectively. These plates 29 and Pitt are generally similar to thosedescribed above in connection with the tunnel dryer. The plates 29 and30, therefore, include a relatively larger number of air passages ororifices 31 which have been found to provide for the vastly improvedcontrol of the air flow.

The product to be dried is fed into the chamber 21 through spray nozzles32 and preferably by an array of two or more nozzles 32 mounted inspaced position beyond the inlet orifice plate 22. These nozzles 32 areconventional atomizing nozzles for spraying the liquid product to bedried into the hot air stream. The nozzle array illustrated has fourseparate nozzle 32 spaced in a symmetrical pattern with each of thenozzle 32 being positioned adjacent to a corner of the inlet orificeplate 29. The nozzles 32 are shown connected to a convenient source ofthe liquid being dried through a pump 33. It has been found that thelaminar flow of the drying air provides for a significantly improvedevaporative efficiency which permits the product to be thoroughly driedin a shorter time and at a uniform and lower chamber temperature sinceno cool areas have to be compensated for. This also provides for areduction in the B.t.u. demand for air heating thereby saving fuel. Thedrying chambers in a tunnel of the type illustrated, for example, fortypical powdered egg products, may be in the neighborhood of 130 F.where the outlet stream has a relative humidity in the neighborhood of30 percent. To produce this tunnel temperature a typical air inputtemperature in advance of the spray nozzles 32 will be about 320 F.since the spraying cools the air at this zone.

As the sprayed product dries in the chamber 21, it falls to the chamber21 bottom. A belt-type drag is illustrated having drag bars 35 connectedat their ends to endless side drive belts or chains 36 so that bars 35continuously remove the dried product from the drying chamber 21. Dragbars 35 carry the product into a well 37 which accommodates a helicoil38 for removing the dried product from the dryer.

The orifice plate controlled laminar drying air flow which provides theimproved results, already described above, is also useful in anotherform of dryer having a vertical drying chamber. This improvement of theinvention is illustrated in FIGS. 7 and 8. In this dryer 40, a generallycylindrical vertical drying chamber 41 is mounted between a conical hotair inlet 42 at the top of the chamber 41 and a conical product outlet43 at the bottom of the chamber 41. The dried product in this embodimentpasses through a discharge outlet 44 including an air lock 44' while theexhaust air is passed through a suitable cyclone separator 45 andexhaust blower 58 mounted adjacent to the chamber 41 and including aproduct outlet 46 also having an air lock 46' which adds the driedpowder separated at that point to the product being fed by an auger 59to the main outlet 47. This dryer also includes inlet and outlet orificeplates 48 and 49, respectively, including a series of spaced orifices 50and 51 for causing the drying air to flow in its preferred uniform orlaminar flow pattern. The circular cross section of the tunnelillustrated is found to operate efficiently with a single product spraynoule 52 although other nozzle patterns may be used. The hot drying airis fed through a blower 53 from a heater 54 and filter 55 and the liquidproduct which is being dried is pumped from a product source by a liquidpump 56 coupled to the spraying nozzle 52. This dryer utilizes gravityforce to facilitate product movement and collection and includes arotary wiper 57 to insure the passage of the dried powder through thelower orifice.

It can be seen from the foregoing that the improved air control of thisinvention allows tunnel and chamber types of dryers and blast freezersto operate more efficiently by providing for uniform cross-sectional airflow throughout the drying chambers. The uniform air flow insures aneven heating and drying of product regardless of its cross-sectionalposition in the chamber, thereby permitting even and lower dryingtemperatures and providing a better product and fuel savings.

As various changes may be made in the form, construction and arrangementof the parts herein and the particular methods described withoutdeparting from the spirit and scope of the invention and withoutsacrificing any of its advantages, it is to be understood that allmatter herein is to be interpreted as illustrative and not in a limitingsense.

Having thus described my invention, I claim: 1. In an improved spraydrying chamber having an elongated horizontal drying chamber extendingbetween an air inlet and an air outlet and having a plurality of spraynozzles beyond said air inlet and a drag means on the chamber floor forremoving dried powder in advance of said air outlet the improvementcomprising a first air flow controlling plate positioned in the air pathintermediate said air inlet and said nozzles, a second air flowcontrolling plate positioned in the air path between said drag means andsaid air outlet, and said first and second plates having uniformlyspaced orifices throughout for causing a uniform air flow throughout thecross sections of said chamber and providing a low air pressure dropalong said chamber as compared with the air pressure drop across saidplates.

2. In an improved spray drying chamber having a generally verticaldrying chamber extending between an upper air inlet and a lower airoutlet and having a downwardly directed spray nozzle axially positionedbelow said air inlet for concurrent flow of air and sprayed liquid, theimprovement comprising a first air flow controlling plate positionedtraversely across air path intermediate said air inlet and said nozzle,a second air flow controlling plate positioned traversely across the airpath above said air outlet, and said first and second plates havinguniformly spaced orifices throughout for causing a uniform air flowthroughout the cross sections of said chamber and providing a low airpressure drop along said chamber as compared with the air pressure dropacross said plates.

1. In an improved spray drying chamber having an elongated horizontaldrying chamber extending between an air inlet and an air outlet andhaving a plurality of spray nozzles beyond said air inlet and a dragmeans on the chamber floor for removing dried powder in advance of saidair outlet the improvement comprising a first air flow controlling platepositioned in the air path intermediate said air inlet and said nozzles,a second air flow controlling plate positioned in the air path betweensaid drag means and said air outlet, and said first and second plateshaving uniformly spaced orifices throughout for causing a uniform airflow throughout the cross sections of said chamber and providing a lowair pressure drop along said chamber as compared with the air pressuredrop across said plates.
 2. In an improved spray drying chamber having agenerally vertical drying chamber extending between an upper air inletand a lower air outlet and having a downwardly directed spray nozzleaxially positioned below said air inlet for concurrent flow of air andsprayed liquid, the improvement comprising a first air flow controllingplate positioned traversely across the air path intermediate said airinlet and said nozzle, a second air flow controlling plate positionedtraversely across the air path above said air outlet, and said first andsecond plates having uniformly spaced orifices throughout for causing auniform air flow throughout the cross sections of said chamber andproviding a low air pressure drop along said chamber as compared withthe air pressure drop across said plates.